Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be accessed by various types of access terminals adapted to facilitate wireless communications, where multiple access terminals share the available system resources (e.g., time, frequency, and power).
An access terminal may include a subscriber identity module (SIM), or in some examples, an application (e.g., SIM application) that runs on a universal integrated circuit card (UICC), which stores the identification information (e.g., international mobile subscriber identity) of the access terminal and the other information used to identify and authenticate the subscriber of the access terminal. The SIM, UICC, and/or the applications running on the UICC may be referred to as the SIM or SIM card in this disclosure. A multi-SIM access terminal holds two or more SIM cards (or runs two or more SIM applications), and allows the use of two or more services or subscriptions on the same access terminal. In one example, an access terminal has dual SIMs and allows both SIMs to be active simultaneously such that the access terminal can make calls using either SIM at any given time. A dual SIMs access terminal may be referred to as a dual SIM dual standby (DSDS) access terminal that operate both SIMs simultaneously but shares only one RF chain or transceiver between them. Using each SIM, the access terminal communicates with the corresponding wireless network using a particular communication protocol. Examples of the communication protocols include those defined by the 3rd Generation Partnership Project (3GPP), including Global System for Mobile Communications (GSM), Universal Mobile Telecommunications Systems (UMTS), Long-Term Evolution (LTE, also known as the Evolved Packet System or EPS); as well as those defined by the 3rd Generation Partnership Project 2 (3GPP2), including CDMA2000 1×. Evolution Data Optimized (EVDO), etc. Of course, those of ordinary skill in the art will recognize that any suitable communication protocol may be utilized within the scope of the present disclosure, without being limited to those examples described above.
An access terminal, while engaged in a call using a first communication protocol (e.g., EVDO), may perform tune-away operations, e.g., tuning to a channel of a second communication protocol (e.g., GSM or 1×) for every predetermined cycle or period. After receiving, for example, signaling on the second communication protocol, the access terminal tunes back to continue the call using the first communication protocol. The first communication protocol and second communication protocol may correspond to the same SIM or different SIMs. While performing these tune-away operations, however, the access terminal typically performs data ramp-down and ramp-up procedures for the first communication protocol traffic before and after tune-away. That is, before the tune-away, the access terminal reduces (ramp-down) its transmission packet sizes, and after the tune-away, the packet sizes are increased back up (ramp-up) again. The ramp-up and ramp-down operation may undesirably impact the data throughput of the call using the first communication protocol.